This invention relates generally to residential furnaces and, more particularly, to the use of thermal insulation in a heat exchanger housing for reducing the level of noise emanating from the furnace.
In order to increase the efficiency of a residential furnace, thermal insulation is generally applied to the inner side of the furnace casing to reduce the heat loss that would otherwise occur. Current furnaces generally apply a two layered insulation structure on the furnace interior walls surrounding the heat exchanger compartment to reduce the heat loss. The outer layer of the insulation structure is commonly a fiberglass blanket, and the inner layer is commonly a thin covering sheet of an aluminum foil material. The cover layer serves two purposes: to reduce thermal loss by reflecting heat back from the walls of the furnace casing and to prevent glass fiber in the outer layer from flowing into the ventilation duct.
The noise from a furnace typically originates from these primary sources: the blower that passes air over the heat exchangers, the inducer that draws air into the heat exchanger and the burners that introduce fuel/air mixtures to be ignited at the entrance to the heat exchanger cells. Generally, as the heating capacity is increased, so is the noise that is created.
Although efficiency of a furnace is considered to be very important to the homeowner, furnace noise, caused in a large part by the blower in passing the return air through the heat exchanger compartment and into the ventilation ducts, is also a concern to the homeowner. Accordingly, a small sacrifice in efficiency may be readily accepted for a substantial reduction in the amount of noise emanating from the furnace into the ducts.